crypto: add support for PBKDF2 algorithm

The LUKS data format includes use of PBKDF2 (Password-Based
Key Derivation Function). The Nettle library can provide
an implementation of this, but we don't want code directly
depending on a specific crypto library backend. Introduce
a new include/crypto/pbkdf.h header which defines a QEMU
API for invoking PBKDK2. The initial implementations are
backed by nettle & gcrypt, which are commonly available
with distros shipping GNUTLS.

The test suite data is taken from the cryptsetup codebase
under the LGPLv2.1+ license. This merely aims to verify
that whatever backend we provide for this function in QEMU
will comply with the spec.

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

1 files changed, 152 insertions, 0 deletions

diff --git a/include/crypto/pbkdf.h b/include/crypto/pbkdf.h
new file mode 100644
index 0000000000..58a1fe62a1
--- /dev/null
+++ b/include/crypto/pbkdf.h
@@ -0,0 +1,152 @@
+/*
+ * QEMU Crypto PBKDF support (Password-Based Key Derivation Function)
+ *
+ * Copyright (c) 2015-2016 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef QCRYPTO_PBKDF_H__
+#define QCRYPTO_PBKDF_H__
+
+#include "crypto/hash.h"
+
+/**
+ * This module provides an interface to the PBKDF2 algorithm
+ *
+ *   https://en.wikipedia.org/wiki/PBKDF2
+ *
+ * <example>
+ *   <title>Generating an AES encryption key from a user password</title>
+ *   <programlisting>
+ * #include "crypto/cipher.h"
+ * #include "crypto/random.h"
+ * #include "crypto/pbkdf.h"
+ *
+ * ....
+ *
+ * char *password = "a-typical-awful-user-password";
+ * size_t nkey = qcrypto_cipher_get_key_len(QCRYPTO_CIPHER_ALG_AES_128);
+ * uint8_t *salt = g_new0(uint8_t, nkey);
+ * uint8_t *key = g_new0(uint8_t, nkey);
+ * int iterations;
+ * QCryptoCipher *cipher;
+ *
+ * if (qcrypto_random_bytes(salt, nkey, errp) < 0) {
+ *     g_free(key);
+ *     g_free(salt);
+ *     return -1;
+ * }
+ *
+ * iterations = qcrypto_pbkdf2_count_iters(QCRYPTO_HASH_ALG_SHA256,
+ *                                         (const uint8_t *)password,
+ *                                         strlen(password),
+ *                                         salt, nkey, errp);
+ * if (iterations < 0) {
+ *     g_free(key);
+ *     g_free(salt);
+ *     return -1;
+ * }
+ *
+ * if (qcrypto_pbkdf2(QCRYPTO_HASH_ALG_SHA256,
+ *                    (const uint8_t *)password, strlen(password),
+ *                    salt, nkey, iterations, key, nkey, errp) < 0) {
+ *     g_free(key);
+ *     g_free(salt);
+ *     return -1;
+ * }
+ *
+ * g_free(salt);
+ *
+ * cipher = qcrypto_cipher_new(QCRYPTO_CIPHER_ALG_AES_128,
+ *                             QCRYPTO_CIPHER_MODE_ECB,
+ *                             key, nkey, errp);
+ * g_free(key);
+ *
+ * ....encrypt some data...
+ *
+ * qcrypto_cipher_free(cipher);
+ *   </programlisting>
+ * </example>
+ *
+ */
+
+/**
+ * qcrypto_pbkdf2_supports:
+ * @hash: the hash algorithm
+ *
+ * Determine if the current build supports the PBKDF2 algorithm
+ * in combination with the hash @hash.
+ *
+ * Returns true if supported, false otherwise
+ */
+bool qcrypto_pbkdf2_supports(QCryptoHashAlgorithm hash);
+
+
+/**
+ * qcrypto_pbkdf2:
+ * @hash: the hash algorithm to use
+ * @key: the user password / key
+ * @nkey: the length of @key in bytes
+ * @salt: a random salt
+ * @nsalt: length of @salt in bytes
+ * @iterations: the number of iterations to compute
+ * @out: pointer to pre-allocated buffer to hold output
+ * @nout: length of @out in bytes
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Apply the PBKDF2 algorithm to derive an encryption
+ * key from a user password provided in @key. The
+ * @salt parameter is used to perturb the algorithm.
+ * The @iterations count determines how many times
+ * the hashing process is run, which influences how
+ * hard it is to crack the key. The number of @iterations
+ * should be large enough such that the algorithm takes
+ * 1 second or longer to derive a key. The derived key
+ * will be stored in the preallocated buffer @out.
+ *
+ * Returns: 0 on success, -1 on error
+ */
+int qcrypto_pbkdf2(QCryptoHashAlgorithm hash,
+                   const uint8_t *key, size_t nkey,
+                   const uint8_t *salt, size_t nsalt,
+                   unsigned int iterations,
+                   uint8_t *out, size_t nout,
+                   Error **errp);
+
+/**
+ * qcrypto_pbkdf2_count_iters:
+ * @hash: the hash algorithm to use
+ * @key: the user password / key
+ * @nkey: the length of @key in bytes
+ * @salt: a random salt
+ * @nsalt: length of @salt in bytes
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Time the PBKDF2 algorithm to determine how many
+ * iterations are required to derive an encryption
+ * key from a user password provided in @key in 1
+ * second of compute time. The result of this can
+ * be used as a the @iterations parameter of a later
+ * call to qcrypto_pbkdf2().
+ *
+ * Returns: number of iterations in 1 second, -1 on error
+ */
+int qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
+                               const uint8_t *key, size_t nkey,
+                               const uint8_t *salt, size_t nsalt,
+                               Error **errp);
+
+#endif /* QCRYPTO_PBKDF_H__ */